Method of controlling deoxidation of steel and adding alloys thereto



Patented Mar. 21, 1950 METHOD OF CONTROLLING DEOXIDA- TION OF STEEL AND ADDING ALLOYS THERETO Frederick H. Meng, tl ilyria, and John D. Tyson, Lorain, .Ohio, assignors to National Tube Company, a-corporation of New Jersey No Drawing. Application June 3, 1948,

Serial No. 30,988

2 Claims.

This invention relates to the practice of steelmaking in the open-hearth furnace and, in particular, to the control of deoxidation and the ad' dition of alloys.

The principal object of the invention is to improve on existing open-hearth practice in order to increase production, particularly in respect to deoxidation and alloy additions. A further object is to reduce the time required for finishing a heat of steel and to increase the efficiency of the alloys added to the molten steel.

It is customary and generally considered desirable in the manufacture of certain'types of basic open-hearth steels, to add a preliminary 'deoxidizer to the steel bath as a block when approximately the carbon content desired at tapping has been reached. This effect has heretofore been usually accomplished by adding lump ferrosilicon (-15% Si), or spiegel to the steel bath. These alloys sink slowly through the slag and are then quickly fused by th molten metal, effecting suificient deoxi-dation, that is, preferentially combining with the oxygen available in the bath, to arrest or retard the carbon-oxygen reactions in the steel to permit tapping of the furnace without any further appreciable loss in carbon. At the same time, the detrimental effect of oxygen in the steel on the efilciencies of alloy addltions is reduced, Alloys in the amount needed for the desired final analysis are generally added after several minutes are allowed for solution of the block.

Another method advocated for obtaining the blocking effect is by shoveling finely ground (8 mesh) ferrosilicon (50% Si or above) onto the slag before alloy additions are made. It is believed that the slag is deoxidized in this way, thus retarding the action between slag and metal (Herty Patent No. 2,361,627)

Still another method advocated for obtainin the blocking efiect involves the use of silicomanganese Si) dumped into the furnace at approximately the carbon content desired at tapping. The manganese content of the steel bath is increased by this addition. If the required final analysis of the steel calls for more manganese content than that obtained by the silico-manganese used as a block, this difference is usuall made up by adding ferromanganese to the furnace several minutes after the block.

We have found that lump ferrosilioon (50% Si or better) when used in conjunction with the final ferro-alloy additions accomplishes the desired blocking eiTect with certain benefits not obtained by the other methods. In a present preierred practice ofour method, lump ierrosili-con (50% Si or better, preferably in 3 pieces or larger) is .used in amounts approximating 4% pounds per net ton of steel tapped from the furnace (750 lbs. per heat of net tons) The ferrosilicon is spread over the top of a ferro-alloy, such as ferromanganese, in the charging box used for making the final alloy addition at the desired tapping carbon. Thus, when the charging box is turned over into the furnace and the contents are dumped, the heavier or denser ferromanganese, being above the ferrosilicon, drives the latter through the slag and down deep into the metal. As a result of this, the deoxidizing or blocking? reaction is rapid. By the simultaneous addition of the ferro-alloys, a saving of some minutes is realized in the completion of each basic openhearth heat requiring a block, over and above the prior methods involving a separate addition of the ferro-alloys subsequent to the addition of a blocking material to the bath or to the slag.

The ferro-alloys which are added to the bath are themselves deoxidants, although rather expensive ones, and it might appear that the time saved in bringing a heat to the condition for tapping would be more than offset b the loss of ferr c-alloys to the slag through the deoxidation reaction. Instead, there appears to be some 00- .operative action between the materials whereby a greater solution of the ferro-alloys in the steel is obtained than when the ferro-alloys are added separately in the known manner. While the exact reasons for this unusual and beneficial result are not known, it may well be that, with the described method, the heat of reaction of the ferrosilicon with the oxygen in the steel simultaneously speeds solution of the ferro-alloys. Possibly for this reason, better results are obtained with lump ferrosilioon containing 50% Si, as compared with lump ferrosilicon containing 10-15% Si, because of the lower mass of iron involved for a given reactive silicon addition. Possibly silicon is more free to combine with the oxygen, through its greater concentrations in the steel, because it is not intimately associated with manganese, as is the case when silico-manganese is used.

Another advantage which results from driving the ferrosilicon deep down into the steel bath with the ferro-alloys and efiecting a more rapid reaction is that tendencies toward phosphorus reversions from slag to metal are greatly diminished. Although it would appear that lump ferrosilicon (50% Si or better), by virtue of its specific gravity, would pass through the slag and into the metal, it is quite likely that it is carried much deeper into the metal and passes through the slag much more quickly when added according to our practice. In this manner,solution of the ferrosilicon and resultant reaction of silicon with oxygen is started deep in the bath and has probably gotten well under "way by *the time these lumps float to the slag metal interface. It does not seem likely that the ferrosilicon would be carried as deep into the bath if mixed with ferro-alloys or placed in the charging box so thatwhen it is dumped, the ferrosilicon enters the steel last, as when driven down by the heavier or denser ferromanganese according to our invention.

It is highly desirable, in finishing a heatoi basic open-hearth steel, that the lime-silica ratio be disturbed as little as possible at the time of tapping to minimize the possibility of phosphorus reversion, and it is believed that our method of blocking with silicon alloys is least disturbing to this ratio. r 4

II In, addition to the above advantages of our invention, the practice thereof iIlYOlVESlIlQfimpfilI- mentof 'stee'l quality. ,j I I The beneficial results obtainable by the "invention are revealed in the improved ferromanganese 5 e'iiiciencies obtained in actual practice. This 'e'flicie'n'cy is the ratio of manganese recovered in the steel to total manganese available. I While We have described only a preferred practice of our invention, changes in th procedure disclosed may be made within the scope of the appended claims.

We claim:

1. In the manufacture of steel by the openhear'th process, the steps of dumping into the bath simultaneously, after approximately the desired carbon content has been reached, a layer of a ferro-alloy disposed above a layer of lump ferrosilicon containing at least 50% silicon, said I ferro-alloy having a density greater than that of REFERENCES CITED The following references are of record in the file of this patent:

The Physical Chemistry of Steel Making: Deoxidation of Open-Hearth Steel with Manganese Silicon Alloys-Cooperative Bulletin 58, published by Mining and Metallurgical Advisory Boards (1932),pages 15-47, 20 and 6l63.

Basic Own Hearth Steelmaking, published by the American Institute of Mining and Metallurgical Engineers '(1'944), pages 111-113, 230 and 231. 

2. IN THE MANUFACTURE OF STEEL BY THE OPENHEARTH PROCESS, THE STEPS OF LOADING A CHARGING BOX WITH A LAYER OF A FERRO-ALLOY AND THEN A LAYER OF FERROSILICON CONTAINING AT LEAST 50% SILICON, SAID FERRO-ALLOY HAVING A DENSITY GREATER THAN THAT OF THE FERROSILICON, AND INVERTING THE BOX ABOVE THE BATH AFTER APPROXIMATELY THE DESIRED CARBON CONTENT HAS BEEN REACHED, WHEREBY THE FERRO-ALLOY DRIVES THE FERROSILICON BELOW THE SURFACE OF THE BATH. 